This WILL be overturned.
Don't bet on it. His silence in the situation was relevant evidence independent of any statement of incrimination. It is one thing to button your lip, but it is entirely another thing to act indifferent to people who are dead or dying in a car wreck in which you were involved.
That was the issue. And that is why it is a correct ruling.
As a full-on Communist Collective, California will find a way around it.
Hell, they just might set up checkpoints at the border and a Berlin Wall, and ignore the ruling altogether.
Probably not...